Grouping dogs according to their post-ACTH cortisol concentration during trilostane therapy, revealed 9 dogs with post-ACTH cortisol between 41 and 138 nmol/L (group 1) and 5 with post-ACTH cortisol <41 nmol/L (group 2, no clinical signs of hypocortisolism evident). The gene discussed is POMC; the disease is adrenocortical insufficiency.